This type of radar is known in the art as SSR and we shall use this abbreviation for convenience.
It is a known fact that an SSR can detect aircraft equipped with transponders by decoding relevant replies, measure the time of arrival and the azimuthal angle of arrival and locate the aircraft.
The device which is the subject of this invention, refers to the azimuthal angle measurement problem, for which a very high accuracy is required so as not to incur excessively large aircraft location errors, especially at large detection ranges.
Until now, the high accuracy has been achieved by the use of monopulse receivers. Such receivers can evaluate the azimuth of each return pulse by comparing the signals received by two antenna patterns referred to, respectively, as (.SIGMA.) and (.DELTA.).
For information purposes, a few well-known works related to a number of monopulse receivers and to the relevant reasons for the error of concern are mentioned:
G. Jacovitti: "Performance Analysis of Monopulse Receivers for secondary surveillance Radar, IEEE Trans. On Aerospace & Electronic Systems, vol. AES-19, No 6 November 1983, pp. 884-897.
The device in question is particularly applicable to amplitude comparison receivers, called L1 in the Jacovitti article.
R. J. Plant, M. C. Stevens: "A Practical Application of Monopulse Processing to the solution of SSR Problems, International Conf. of Radar, Paris, May 21/24, 1984 pp. 56-60; and
G. Galati, C. Benedetti, E. Giaccari, M. Momo: "The Evolution of SSR" Proceedings of the Int. Radar symp. India (IRSI-83) Oct. 9-12, 1983 Bangalore, pp. 416-423.